Re: [PATCH 1/2 v2] serial: mctrl_gpio: Check if GPIO property exisits before requesting it

Mika Westerberg
2019-05-24T10:20:13Z

On Fri, May 24, 2019 at 11:48:24AM +0200, Stefan Roese wrote:
> This patch adds a check for the GPIOs property existence, before the
> GPIO is requested. This fixes an issue seen when the 8250 mctrl_gpio
> support is added (2nd patch in this patch series) on x86 platforms using
> ACPI.
>
> Here Mika's comments from 2016-08-09:
>
> "
> I noticed that with v4.8-rc1 serial console of some of our Broxton
> systems does not work properly anymore. I'm able to see output but input
> does not work.
>
> I bisected it down to commit 4ef03d328769eddbfeca1f1c958fdb181a69c341
> ("tty/serial/8250: use mctrl_gpio helpers").
>
> The reason why it fails is that in ACPI we do not have names for GPIOs
> (except when _DSD is used) so we use the "idx" to index into _CRS GPIO
> resources. Now mctrl_gpio_init_noauto() goes through a list of GPIOs
> calling devm_gpiod_get_index_optional() passing "idx" of 0 for each. The
> UART device in Broxton has following (simplified) ACPI description:
>
> Device (URT4)
> {
> ...
> Name (_CRS, ResourceTemplate () {
> GpioIo (Exclusive, PullDefault, 0x0000, 0x0000, IoRestrictionOutputOnly,
> "\\_SB.GPO0", 0x00, ResourceConsumer)
> {
> 0x003A
> }
> GpioIo (Exclusive, PullDefault, 0x0000, 0x0000, IoRestrictionOutputOnly,
> "\\_SB.GPO0", 0x00, ResourceConsumer)
> {
> 0x003D
> }
> })
>
> In this case it finds the first GPIO (0x003A which happens to be RX pin
> for that UART), turns it into GPIO which then breaks input for the UART
> device. This also breaks systems with bluetooth connected to UART (those
> typically have some GPIOs in their _CRS).
>
> Any ideas how to fix this?
>
> We cannot just drop the _CRS index lookup fallback because that would
> break many existing machines out there so maybe we can limit this to
> only DT enabled machines. Or alternatively probe if the property first
> exists before trying to acquire the GPIOs (using
> device_property_present()).
> "
>
> This patch implements the fix suggested by Mika in his statement above.
>
> Signed-off-by: Stefan Roese <sr@denx.de>
> Cc: Mika Westerberg <mika.westerberg@linux.intel.com>

Reviewed-by: Mika Westerberg <mika.westerberg@linux.intel.com>